Moiré fringes

This review paper clarifies the characteristics of the incoherent-and-multiplicative type moiré fringe phenomenon, presents examples of the application of these characteristics to measurement and explains the profile prediction method and the sharpening conditions of moiré fringes formed by two binary gratings.     

Moiré interferometric fringe patterns about crack tips: Experimental observations and numerical simulation

The local deformation about fatigue cracks has been investigated by the coherent optics method of moiré interferometry. The complexity of the interference fringe patterns motivated the parallel development of companion numerical models for simulating moiré interferometric response for known boundary conditions. Experimental patterns are here examined in the light of computer-generated fringe systems for a stationary crack in elastic as well as elastic-plastic solids. Various effects due to material plasticity, specimen-dependent non-singular stress, and mixed mode loading are identified in the fringe patterns.     

Moiré fringes in metrology

Moiré fringe phenomena have been exploited in a wide range of transducers, particularly in the field of engineering metrology. Paying particular attention to developments which have taken place during the last 15 years, the paper presents a cross-section of moiré techniques for the measurement of displacement, surface topography, deformation, vibration and refractive index gradient.     

Moiré topography in odontology

For several decades, measurement of optical techniques has been used in different branches of science and technology. One of these techniques is the so-called moiré topography (MT) that enables the accurate measurement of different parts of the human body topography. This investigation presents the measurement of topographies of teeth and gums using an automated system of shadow moiré and the phase shift method in an original way. The fringe patterns used to compute the shape and the shape matrix itself are presented in the article. The phase shift method ensures precisions up to the order of microns. Advantages and disadvantages of using the MT are included. Besides, some positive and negative aspects concerned with the implementation of this technique in odontology are shown in the article.     

Computer Aided Moiré Methods

Computer aided moiré methods (CAMM) use the versatility of the computer to manipulate gratings rapidly, the basis of all moiré methods. Application of CAMM to moiré teaching, in-plane moiré, shadow and projection moiré and reflection moiré are reviewed in this paper.     

Moiré methods in interferometry

The applications of moiré methods to optical interferometry are reviewed. They are used for instrumental error subtraction, reduction of spatial frequency of interferogram fringes, increase of sensitivity and the range of applications of interferometric methods, and various information processing operations. The cases of the reference beam and shear type interferometry are treated separately.     

Moiré interferometry for strain analysis

Moiré interferometry is a sophisticated optical method for measuring in-plane strain fields. The basic technology for generating interferograms is discussed, along with the reasoning behind the choice of this technique for particular duties. Methods are evaluated for deriving useful data from interferograms. A range of applications is described, and the various limitations of the method are outlined.     

Focused ion beam Moiré method

A focused ion beam (FIB) Moiré method is proposed to measure the in-plane deformation of object in a micrometer scale. The FIB Moiré is generated by the interference between a prepared specimen grating and FIB raster scan lines. The principle of the FIB Moiré is described. The sensitivity and accuracy of deformation measurement are discussed in detail. Several specimen gratings with 0.14 and 0.20 μm spacing are used to generate FIB Moiré patterns. The FIB Moiré method is successfully used to measure the residual deformation in a micro-electro-mechanical system structure after removing the SiO₂ sacrificial layer with a 5000 lines/mm grating. The results demonstrate the feasibility of this method.     

Moiré interferometry for deformation measurement

Moiré interferometry utilizes high frequency gratings to contour displacement components with a sensitivity of the order of 0·5 μ. This paper briefly reviews the technique for in-plane deformation measurement and its current applications to analyze adhesive bonded joints and composite deformation. The modified set-up for out-of-plane displacement measurement is described and used for fracture mechanics studies and vibration analysis. Finally, a set-up for simultaneous measurement of all three displacement components is described.     

Moiré topography using developed recording methods

Where moiré topography is used to record the shape of objects of approximately cylindrical form or that of a series of such objects, a scanning method with a slit camera can be employed. One such method takes photographs by combining conventional shadow type and projection type moiré topography with a slit camera. Laser methods of line projection combined with a scanning method developed from the projection type of moiré topography are also utilised. The main features of the latter method are that it is not affected by any diffraction effect caused by the grid and that highly accurate recording can be achieved with excellent image quality using the properties of the laser beam. Another distinct advantage is that it is capable of recording the shape of a self-luminous object without contacting by selection of laser wavelenghts and matching optical filters. The laser scanning method can therefore be considered to have considerable potential for future applications.     

Moiré deflectometry—ray tracing interferometry

A method for ray deflection mapping, moiré deflectometry, which is fully compatible with interferometry, is described and demonstrated by numerous examples, including testing of optical components, visualization of flow, study of transient phenomena, and modulation transfer function analysis. Unlike interferometry, moiré deflectometry is a pure ray tracing technique and, therefore, the analysis of three- dimensional objects is greatly simplified. Although the ray tracing approach to optical systems is much older than wave theory, moiré deflectometry seems to be the first attempt to apply ray tracing methods systematically to optical metrology. Moiré deflectometry is fully quantitative, interferometry-compatible in accuracy and has the additional advantage of tunable sensitivity.     

Moiré gauging by projected interference fringes

The formation of Moiré patterns by doubly exposed photographs of projected interference fringes is analysed in detail. The possible applications of these patterns for the measurement of surface deformation and vibration, phase object visualization and height contouring are examined theoretically and experimentally.The described methods are closely related to holographic techniques, but they are usually simpler and applicable in unfavourable environments.     

Deformation measurement using high resolution Moiré photography

By installing a slotted mask inside the lens of a 35 mm camera the response can be tuned to resolve 300 lines/mm. The camera is used to record changes in fine grid patterns applied to engineering structures and by analysing the processed negatives in a spatial filtering system, moiré fringe maps are generated representing in detail the separate x and y displacements that have occured. Measurements have been obtained from materials ranging from concrete to soft plastics and a variety of patterns is described for treating most surfaces.     

Moiré technique in 3-D machine vision

Moiré technique using projected fringes is a promising method in 3-D machine vision for the mapping of surface profiles of objects compared to ideal masters. This paper describes a CAD-integrated system using a CCD camera and a digital image processor. Applications to industrial inspection of CAD-generated master objects are presented.     

Applications of Moiré topography measurement methods in industry

Moiré topography is able to determine the shape of an object, by pattern measuring, in a short time. Recently moiré topography has been used in various industrial fields because it has superior features that point measurement doesn't have. As it becomes popular various related techniques that fit specific needs have been developed and there is the prospect that moiré topography will become a more important measurement method and strengthen its position in the near future.

This paper explains the grid irradiation method and the grid projection method as the basis of the moiré topography measurement method and describes the existing status and prospects of utilizing moiré topography measurement in the applied fields of shape measurement, flatness measurement and detection of abnormality.     

Moiré topography: alternative technique in health care

The instrumentation and application of moiré topography in the diagnosis of corporal asymmetries associated to different illnesses of the osseous-muscular system in early ages is presented in this paper. A sample comprising 203 adolescents ranging between 12 and 15 years were studied. Some moiré topography analysis of human legs and the sole of the foot are also given as examples of moiré applications. The results show the advantages of using this technique in the health care and treatment of different illnesses in adolescents. Some of these advantages are provided by the easy diagnosis and the low cost of the moiré technique.     

Moiré displacement measurement technique for a linear encoder

The light intensity diffracted from superimposed dual transmission gratings is sensitive to their relative lateral displacement but is also affected by changes in the air gap between them. Averaging the diffracted light intensities obtained in the gap range of a Fourier image distance, the resultant intensity was almost independent of the gap between the two gratings and had a period of half the pitch of the grating for the lateral displacement. This method can be used for a linear encoder in precision machining.     

Whole-field analysis of uniaxial tensile tests by Moiré interferometry

Moiré interferometry—a high sensitivity whole-field optical technique—was used to follow the evolution of the deformation process of an aluminium sample subjected to a uniaxial tensile test. This technique allowed us to measure the two in-plane displacement components undergone by the sample, to evaluate the strain, stress and rotation fields, and to appreciate the trends in the deformation pattern that characterized the different stages of the test. Through a subtraction process between fields obtained at two different load levels, we were able to identify the area where strains began to localize and to observe the appearance of the diffuse neck.